How hot is Drogon's fire? Where did the walking dead come from? What disease inspired greyscale? And where can you find dragonglass? A few scientific questions that arose during the seventh season of Game of Thrones

The seventh season of Game of Thrones has come to an end, and it will be a year and a half before we will see winter in Westeros once again. So to ease are anticipation, here are some scientific thoughts on what we saw this past season.

The walking dead

During the last season we have felt the threat of the walking dead from the north more than ever. We had the opportunity to see them fight, kill and even die. The zombies on Game of Thrones seem very different than those we are used to seeing on screens, from "The Night of the Living Dead" to "The Walking Dead". They do not eat brains or corpses; head amputation or a knife to the brain do not stop them; they do not transmit "the disease" to anyone they bite; and they are completely controlled by the White Walkers (or "the Others"), who created them, to such a degree that they die when their White Walker dies.

One may claim that they are not zombies at all, and evidently, they are called "wights" both in the books and in the series. However, if we were to look into the source of the belief in the living dead, we would discover that the original zombies resembled George Martin's more than those of George Romero.

Zombies first appeared as part of voodoo religion in Haiti in the 18th century. According to the belief, voodoo sorcerers can breathe life into the dead, but before doing so, they trap the spirit of the dead person in a jar or container. The resurrected person cannot speak, has no memory and is easy to control. Sorcerers may use these zombies for agricultural or construction work. They are not considered particularly dangerous, and definitely not contagious. In addition, letting them eat salt would bring back their memory and ability to speak. When the sorcerer dies, the zombies return to their village or burial site and die (remind you of anything?).  

Over the years, there were supposedly some cases of people that returned to their village years after being dead and buried. It was claimed that during all of that time they served as zombies for the sorcerer. It is plausible that most, if not all, of these people were frauds, trying to impersonate someone else, but some researchers think there might be a scientific explanation to the zombies from Haiti.

Wade Davis proposed that it was not that the sorcerers were bringing people back to life; but that they make living people seem dead. He claims they do this using tetrodotoxin, the toxin of the Fugu fish. Davis even found traces of this toxin in powders held by the sorcerers.  When the victims are given this powder they become paralyzed, their heartrate slows down and they appear dead, but a few hours later, with or without the assistance of the sorcerer they recover and "return to life". Then, the sorcerer gives them other drugs that may contain Datura, which then impair their consciousness for their entire life as "zombies".

Not everyone accepts Davis's claims. Some researchers doubt that the poison can actually put a person at a death-like state that can be recovered from, and especially that all voodoo sorcerers can administer the exact dosage for this to happen.  

Of course, the White Walkers of Westeros do not need powders and drugs – they wake the dead without even touching them. Their zombies are also much more aggressive than those of Haiti, and it is also much more difficult to kill them.  Their other properties, however, are quite similar.   

ה"רפאים"  של משחקי הכס| צילום מסך מפרק שש של בעונה השביעית, HBO
Wights of Game of Thrones | Screenshot from episode six of season seven, HBO

Breaths of ice and fire?

The breath of fire of the dragons on Game of Thrones, which are actually fire-breathing wyverns, or at least that of Drogon, according to the fourth and fifth episodes of the seventh season, is capable of burning a person to ashes. In order to completely burn a person, including the bones, as it seems Drogon does, a very high temperature is required. Without the bones, a much lower temperature is sufficient.  

Crematories that are used for burning bodies reach temperatures of up to 980 degrees centigrade. The organic materials and water inside the body evaporate, leaving behind not dust, but dry and broken bones. The remains of the bones are crushed to dust using an electric or manual machine after cremation. If we would want to skip the crushing process and make the bones disintegrate without it, it would be worthwhile to try and melt them. The melting temperature of hydroxyapatite, which composes about 70% of bone tissue, is 1,670 degrees centigrade. It is also not certain that this temperature would be sufficient to melt down bone, which is not comprised only of pure hydroxyapatite. It is more plausible that Drogon burned and weakened the bones so that they were destroyed from the fall to ground and from the armor parts that fell on top of them, than that he actually managed to burn them to ashes.

Burning bodies in the crematory takes about two hours, but in the series people were burnt in seconds. The process is probably accelerated due to the large amount of fire in one dragon breath and due the fast flow of hot air.

According to the stories in Westeros, the breath of fire of Balerion, which is Aegon the conqueror's huge black dragon, has been able to melt down the walls of the castle of Harrenhal. Assuming the walls of the castle were made of granite stone, like many castles throughout England, the melting temperature of such walls is around 1,250 degrees centigrade. If they were made from something even more durable, such as rocks rich containing aluminum oxide, the melting temperature would be even higher, reaching about 2,050 degrees. However, Daenerys's dragons are smaller than Balerion. They are neither capable of melting walls nor chains made of iron (1,510 degrees) or steel (about 1,370 degrees, depending on the oxygen percentage). The most they may be able to do is weaken the chains, and for that purpose, only a relatively low temperature, of about 540 degrees is sufficient.

Viserion's death on episode six reveals some of the fire-breathing mechanism in the world of Game of Thrones, and may help estimate the temperature of their breath. When the Night King, which might be Brandon Stark according to the books, throws his ice spear and pierces Viserion's body, some form of flammable gas seems to come gushing out of the wound at the bottom of his neck and above his wing. The gas ignites and explodes, causing the dragon to plummet to his death. It is plausible that the source of the gas is in the sack at the bottom of the dragon's neck. The sack probably stores flammable gases that are produced by the dragon's body under high pressure. This resembles flammable gases, such as methane, that are produced by bacteria in our and other animal's digestive systems.

The color of Drogon's and the other dragons' flames is yellow-orange. If this flame is indeed produced by a carbon-based gas burning in the air, this color is compatible with a temperature of about 1,200 degrees centigrade, which is consistent with the state the dragon breath left the burned bodies and armors at. According to Balerion's abilities, this temperature will rise as the dragons grow larger, unless the breath of fire will be replaced by another power, providing Drogon and Rhaegal join their undead brother.

הפגיעה גורמת לפיצוץ, ככל הנראה של גז דליק. מותו של הדרקון ויסריון | צילום קצר מתוך פרק שש בעונה השביעית של משחקי הכס, HBO
The injury leads to an explosion, probably of flammable gas. The death of Viserion the dragon | Screenshot from episode six of season seven, HBO

In the final scene of the last episode, undead Viserion managed to knock down a part of the large ice wall in the north of Westeros. The wall was built by another Brandon Stark – Bran the Builder – out of steel, dirt and mostly ice. The giants assisted Bran in construction and the children of the forest, who cast strong water spells, reinforced the wall. The mean height of the wall is 213 meters, and it is 480 kilometers long and 90 meters wide. Without the spell, such a structure would collapse, since it would have to face some annoying laws of physics. In addition, the spells of the children of the forest prevent, or have prevented the undead, such as the wights and the White Walkers (the Others) from crossing the wall.

When undead Viserion, whose breath is a blue fire-like force, concentrated his breath in one point, he was able to blow a hole in the wall. How much energy does this actually require?

We approached Dr. Noa Lachman, materials expert from Tel-Aviv University, and asked her to help us estimate the force and power of the dragon's breath.

Before we begin our calculation, we need a little bit of information. The thickness of the wall Viserion blew through is 90 meters. We will regard the entire wall as comprised from pure ice, so a pressure of 25 million pascal, or 25 million newton per square meter, is required to break it.

What is the volume that was broken in? Since we know the height of the wall, we can calculate the diameter of the part of Viserion's breath that hit the wall, as can be observed in the following screenshot. 

קוטר נשיפת הדרקון לעומת גובה החומה | צילום מסך מהפרק השביעי של העונה השביעית, HBO
The diameter of the dragon's breath compared to the height of the wall | Screenshot from episode seven of season seven, HBO

According to this calculation, the diameter is 3.15 meters and the volume of the initial "hole" – the cylinder that is smashed in – is π times 1.575 (half the diameter) squared times 90 (the thickness of the wall), which results in 701 square meters.

The energy required for breaking in a volume like this is 17,525 million newton meters (701 times 25 million) or 17,525 million joules. This energy is equivalent to that produced by an explosion of 4.2 tons of TNT.

Viserion released all of this energy in 34 seconds, making the power of his breath about 515 million joules per second, or 515 megawatts. In more familiar units this is equivalent to about 691 horsepower (or one "dragon-breath power"). 

Dragonglass from the heart of the Earth

"Obsidian. Forged in the fires of the gods, far below the earth. The children of the forest hunted with that, thousands of years ago. The children worked no metal... In place of swords, they carried blades of obsidian." – Maester Luwin, in the book "Game of Thrones".

In our world obsidian is a sort of volcanic glass, which forms when lava from volcanos cools down quickly. One could say Maester Luwin was right: the fire that creates this kind of glass is under the ground, in the house of the god Vulcan.

In contrast, the children of the forest say the "dragonglass" is forged in the fire of dragons. The giant rock made of obsidian under Dragonstone is a strong piece of evidence to support that claim. But, is the fire of dragons strong enough?

Obsidian forms when lava contains a high percentage of silicon dioxide, which is the main ingredient in sand. These rocks melt at a relatively low temperature, less than 900 degrees centigrade. Dragons, as we mentioned earlier, are able to reach these temperatures. We do not know if the glass at Dragonstone was indeed created by the dragons (maybe only Bran could know this), but it seems to be possible at least, as long as they can blow fire for a long-enough time.

The color of obsidian is usually black and it is strong and fragile, with very sharp edges after breaking – much sharper than metal knives. For this reason, it was also used in the real world for making hunting and cutting tools in cultures that existed before the Iron Age. Early Homo species made obsidian knives as early as 1.4 million years ago, and tools made by our species, the Homo Sapiens, have been discovered anywhere from Africa to America. In Israel, obsidian tools thousands of years old were found next to the town of Gilat, in the northern Negev area.  The glass most likely originated in Turkey, and finding it in Gilat indicates the wide-range commerce that was taking place, as well as the importance of this material to the people of the region, since they bothered to import it from so far.

For obvious reasons, we have no way of knowing whether the tools found in our world have magical powers that enable them to kill White Walkers and wights. But, even without superpowers, their physical properties were sufficient in making them very special for the people of the Stone Age.

ראש חץ מאובסידיאן | shutterstock
Arrowhead made from obsidian | Shutterstock

50 scales of grey

Greyscale is a contagious disease and seems to be revolting to the people in the world of Game of Thrones. In a previous article we wrote about it, we mentioned that it is incurable, but in the last season, Samwell Tarly demonstrated that it is not so by curing Jorah Mormont.

The disease is transmitted easily from person to person via skin contact, and can even be transmitted from contaminated animals or objects, like the doll that transmitted the disease to the unlucky princess Shireen Baratheon. Following infection, the disease slowly spreads throughout the body. In the beginning, the only sign is numbness at the infection site, which then spreads to other areas of the body. Then, symptoms resembling the "Israel is drying" campaign begin to appear: the afflicted skin hardens and cracks like dry soil. At more advanced stages, the skin of the infected individual becomes very thick and stiff, turning grey or black. The skin closely resembles grey scales of reptiles, which is where the disease's name came from. Puss accumulates under the scales, indicating the (failing) battle of the body against the greyscale.

If the scales reach the facial area, they may lead to blindness. The final and most awful stage of disease occurs many years after the infected individuals have become "Stone men", covered in scales from top to bottom. At this stage, the disease attacks the internal systems of the infected individuals – the bones, muscles, nervous system etc. Those who survive up to this stage will lose their minds and often become violent.  

Children that contract greyscale may rarely recover from it, leaving only a remnant scar. These children will become immune to the disease and to its much more violent relative the "grey death". Nevertheless, many times they are executed, in fear they will transmit the disease to others. For most people, who have not been exposed to the books that Sam has read, the only way to deal with the disease is through prevention. Since there are no vaccines in Game of Thrones, this is done by enclosing infected areas and killing whoever tries to leave, or by sending the infected individuals to distant "leper colonies".  

Thankfully, in the real world there is no disease with all of the properties of greyscale, but there are a few similar diseases. Leprosy (Hansen's disease), for instance, begins as a skin lesion, and later on develops into various skin growths and peripheral nerve damage that may harm sensation, motion and vision. At advanced stages, the limbs and nose become deformed, along with some other unpleasant phenomena.  In addition, lepers were segregated from society, like those infected with greyscale. Leprosy may have inspired George R. R. Martin's greyscale, but in contrast to it, leprosy is barely contagious. 

In the previous article we mentioned other diseases. For instance, smallpox is a very contagious and deadly disease that can be transmitted through breathing or contaminated objects and leads to many lesions covering the skin. The human papilloma virus (HPV) is another example for a virus that is easily transmitted via skin contact and leads to skin lesions, as well as cancer in certain strains.

However, neither smallpox nor papilloma, or even leprosy does not explain the brain damage that occurs at the final stages of greyscale. A much more fitting disease, with both skin lesions and brain damage is syphilis. This is an extremely contagious and dangerous disease that is transmitted via skin contact, mostly during sexual intercourse or by sharing sex toys, but can also be transmitted via blood and saliva, or even close contact with an afflicted area in the body. At the first stage of syphilis only a skin lesion will appear. The second stage, occurring about two months following infection, a rash appears, as well as small warts on the genitals, joint pain, local hair loss etc. The third stage of syphilis breaks out only after many years. At this stage, the body of the infected individual gradually disintegrates – their nose sometimes falls, they have trouble walking, may become blind, and while their body is deforming and fading away, they lose their sanity.  

Therefore, greyscale is an imaginary disease incorporating leprosy, syphilis and maybe other real-life diseases, which is also much more contagious and deadly than either of them.

Both syphilis and leprosy can be treated with antibiotics, but if nerve damage has already taken place, as well as damage to other organs, it will remain even after successful treatment. In the world of Game of Thrones there are no antibiotics, and the ointment that Sam Tarly applied on Jorah does not have very promising medical properties: it is composed of resin of pine, green bark of elder twigs, white beeswax and oil from the olive. Therefore, it seems that Jorah's recovery happened mainly due to Sam treating him with an especially deep-tissue peel.

How is this possible? We can only guess. Maybe as long as the disease has not spread to internal organs it is enough to simply remove every afflicted piece of skin – like removing a wart – in order to cure the disease, even if it leaves scars. This is probably the reason why amputation of an afflicted organ may halt the greyscale before it spreads on top of the skin – the unknown disease-causing agent spreads near the surface and not inside the body, at least not at first. In addition, the puss that was apparent during the peeling process indicates immune system activation. It may be possible that removal of most of the afflicted and infested areas has allowed Jorah's immune system to finally overcome the disease.   

סאם מטפל במחלה של ג'ורה | צילום מסך מהפרק השני של העונה השביעית, HBO
Sam taking care of Jorah's disease | Screenshot from episode two of season seven, HBO

The perks of being a eunuch

Theon Greyjoy may not be an incredibly skilled or strong warrior, but he has a secret weapon: he is completely resistant to the greatest fear of any other man around, getting hit in the groin. We know Theon has lost his penis while being tortured by Ramsay, and according to the battle he fought in the last episode, we are also pretty certain he also lacks testicles. But, is a eunuch without a penis or testicles really resistant to a blow below the belt?

Most of the pain from a kick to the groin indeed comes from the testicles themselves. The scrotum contains many nerve cells that transmit pain to the brain. Since the testicles are not protected by bone, muscle or a thick layer of fat, it is pretty easy to turn on these nerve cells.

In addition, a blow to this area leads to referred pain, i.e., not only does the area itself ache, but also the abdomen and sometimes more distant areas. The source of the referred pain is usually not in the nerve cells inside the skin, but in more internal cells, in this case, inside the penis and testicles. A strong-enough blow also turns on these internal nerve cells, causing pain in vast areas of the body.

This means that lacking external genitals would indeed reduce the pain of the receiver of a kick to that area. Reduce, but not completely make it disappear, of course – a kick is still a kick, and there are also nerve cells in the pelvis, not to mention a wound that may have remained after the not-so-medical procedure. Therefore, we are not certain if even someone with no genitals could actually stand and smile at the attacker like Theon did, but maybe he is tougher than he looks. If it will help him save Yara, we are definitely for it.

Translated by Elee Shimshoni